The operation of a pneumatic tool is controlled through a push button mounted on the tool. When the push button is depressed, a volume of high-pressure air is introduced into the pneumatic tool to rotate a front working end of the tool, so that works such as tightening or loosening screws that are otherwise usually done manually could now be more efficiently completed.
FIG. 1 is a sectional view of a conventional push button A2 that is designed for mounting on a common pneumatic tool A as schematically shown in FIG. 3. When a main rod A3 of the push button A2 is pushed inward, an amount of high-pressure air supplied via an air hose A1 (see FIG. 3) is quickly introduced into the pneumatic tool A to drive a working element of the tool to work. The operating speed of the working element of the pneumatic tool A completely depends on the air pressure introduced into the tool A. The tool A operates quicker when a higher air pressure is introduced thereinto, and slower when a lower air pressure is introduced. To control the air pressure to be introduced into the tool A, an operator must control the strength of depressing the push button A2 completely according to his own experience or physical feel. It is therefore uneasy for all operators to apply force accurately and uniformly on the push button to obtain a desired operating speed of the pneumatic tool A, particularly when the operator has handled the pneumatic tool A having a considerable weight for a prolonged time and got sore and ached fingers holding the tool A.